The skin, particularly in humans, contains an elaborate network of elastin fibers which are responsible for maintaining its elastic properties. With excessive exposure to sunlight the elastic fiber system becomes hyperplastic, disorganized and ultimately disrupted. This is known as actinic elastosis and is the principal cause of wrinkling, discoloration and laxity of the skin in the exposed areas of the body. The skin can repair itself to some extent but it is nevertheless desirable to have an agent which can accelerate the repair of this prematurely aged skin.
The UVB irradiated hairless mouse has been found to be a convenient model for actinic elastosis in the skin. (Kligman et al. J. Invest. Dermatol. 78:181 (1982). It has been shown by Johnston et al. in J. Invest. Dermatol. 82:587 (1984) that irradiation with low levels of UVB which simulate realistic solar exposure leads to a significant increase in skin elastin as measured by desmosine content. The amount of this amino acid, which is isolated from acid hydrolysis of elastin, is proportional to the elastin present in the skin. (Uitto et al., Lab. Invest. 49:1216 (1973). Treatment of irradiated mice with topical retinoic acid has been shown to normalize the histological features of the skin in which the previously elastotic dermis has the appearance of unirradiated tissue (Kligman et al., Conn. Tissue Res. 12:139 (1984), Kligman U.S. Pat. No. 4,603,146 July 1986). Therefore this model can be used to determine the efficacy of compounds in the repair of sun damaged skin.